The present invention relates to a gas insulated electrical apparatus, and more particularly to a gas insulated electrical apparatus having a particle trap which is a low potential region inside of the hermetic sheath.
FIG. 1 illustrates, in section, one example of a conventional gas insulated electrical apparatus and FIG. 2 illustrates, in section, a sealing structure for hermetically sealing sheaths of the gas insulated electrical apparatus.
Referring to the figures, the conventional gas insulated electrical apparatus comprises a metallic hermetic sheath 1 which is grounded, a high voltage conductor 2, an insulating spacer 3 for insulatably supporting the high voltage conductor 2 within the sheath 1. The hermetic sheath 1 comprises a plurality of sheath sections 1a hermetically connected to each other by means of sealing structures which will be described in more detail later. The high voltage conductors 2 each disposed within each section 1a of the sheath 1 are connected by connectors 4 having shields 5 for shielding each connector 4. An electrically insulating compressed gas 6 is confined within each section 1a of the divided metallic sheath 1.
The gas insulated electrical apparatus further comprises a plurality of sealing structures for hermetically connecting the divided metallic sheath sections 1a to each other. Each sealing structure comprises two flanges 8 integrally formed with the metallic sheath section 1a, and the circumferential flange portion of the insulating spacer 3. The flanges 8 and the insulating spacer 3 have through holes formed in the axial direction thereof and a bolt 9 is inserted into the through holes for hermetically joining them with a nut 9a which is in engagement with the bolt 9.
Each flange 8 is provided on the side surface thereof where the insulating spacer 3 comes in contact with the flange 8 with an annular groove 10 for receiving an O-ring 11 therein. When the flanges 8 and the insulating spacer 3 disposed between the flanges 8 are joined by the bolts 9, each metallic sheath 1 is hermetically sealed by the O-ring 11 in each groove 10 to thereby confine the compressed gas 6 within each sheath section 1a.
However, the thus constructed conventional sheath 1 has problems in that it is difficult to machine the flanges 8 because they are integrally formed with the sheath section 1a. When electrically conductive foreign matters such as metallic powder and dust are present in the sheath 1, the electrically conductive particles adhere to the connecting portion between the flanges 8 and the insulating spacer 3, thereby causing the withstand voltage characteristics of the sheath 1 to be reduced.